HIIT vs LISS

I'm not a fan of the HIIT for health trend and I'd suggest that you probably shouldn't be either. Much of it is based on the idea that you'll get great results whilst saving time, but as you'll have seen in the video, that's probably not as true as we're led to believe.

Intervals have their place in performance training and that's where they belong: Firmly rooted in training to get faster.

A quick summary of my concerns from the video:

Concern #1: Is HIIT really more time-efficient?

Using the really extreme example of the Tabata workout shows that it really isn't for a number of reasons.

• Unless you want to risk injuring yourself or worse, suffering a heart attack or stroke, you need to warm up properly before undertaking any intense interval training. I allowed 10 minutes in the video example. For context, the warm-up for one workout with the Team GB team pursuit squad when I was involved in their sessions was an hour long. That was for 3 intervals that lasted just 5  minutes each!
• You'll also need to cool down properly after your session.
• If you've done the intervals properly (i.e. maximum exertion), you'll almost certainly be lying on the floor in a pool of sweat, gasping for breath. You will not instantly be running to the shower.

Once you add all of that up, plus allow for being a bit shaky for the for an hour or two afterwards, a nice comfortable, moderate 30-minute run is almost certainly more time-efficient.

Longer HIIT intervals will almost certainly be even less time-efficient once you add in warm-ups, cool-downs etc. And once you go beyond a certain duration, it's not HIIT any more anyway.

Concern #2: Is HIIT repeatable?

If you had to do this workout every day, could you? OK, how about every 2 days? Could you do this workout when you're not 100%?

The soreness and stress imposed by intervals makes them something that isn't realistically repeatable over a long period of time. Yes, you could motivate yourself to do this for a few weeks but given time, you'll end up injured or burned out. HIIT is simply not a good approach for baseline cardio.

Low intensity steady state cardio is still accessible, even when you don't feel great. This makes it a repeatable option.

Concern #3: Does HIIT actually burn more calories?

The simple example used, the slide for which is below, illustrates that it doesn't, at least not to a significant degree.

Even if you were able to burn an extra 2kcal per minute on the intervals (20kcal total), given the extra level of discomfort and the mental energy required to motivate yourself to do those intervals, is that tiny bit extra actually worth it?

Concern #4: HIIT is very poorly tolerated

Unless you're a fairly highly trained athlete, intervals are actually very poorly tolerated by most people. The risk of illness and injury is simply too high for me to believe they're a good option for baseline health-related cardiovascular training.

You will always find the outlier who has managed to make a HIIT programme work in the long term. The thing to remember is that there is a "survivorship bias" around stuff like this; very few people will come forward and tell you that their body couldn't take it.

Concern #5: Is the post-exercise calorie burning effect real?

You certainly do seem to burn more calories after an HIIT session than you do after a moderate run. In the study mentioned, the extra effect was just 16 calories. That was just from the intervals, no warm-up or cool-down included, so how good was the effect really?

Surely, the key benefit is from the exercise itself, not from some mystical "afterburn" effect that isn't that big anyway? Once again, consider the extra mental & physical effort expended for what is a tiny increment & that moderate cardio starts to look ever better.